#line 1 "/workspaces/compro/lib/template.hpp"


#line 1 "/workspaces/compro/lib/io/vector.hpp"
#include <iostream>
#include <vector>

#ifndef IO_VECTOR
#define IO_VECTOR

template <class T> std::ostream &operator<<(std::ostream &out, const std::vector<T> &v) {
  int size = v.size();
  for (int i = 0; i < size; i++) {
    std::cout << v[i];
    if (i != size - 1)
      std::cout << " ";
  }
  return out;
}

template <class T> std::istream &operator>>(std::istream &in, std::vector<T> &v) {
  for (auto &el : v) {
    std::cin >> el;
  }
  return in;
}

#endif
#line 4 "/workspaces/compro/lib/template.hpp"
#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < n; i++)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define ALL(v) (v).begin(), (v).end()
#define coutd(n) cout << fixed << setprecision(n)
#define ll long long int
#define vl vector<ll>
#define vi vector<int>
#define MM << " " <<

using namespace std;

template <class T> void chmin(T &a, T b) {
  if (a > b)
    a = b;
}

template <class T> void chmax(T &a, T b) {
  if (a < b)
    a = b;
}

// 重複を消す。計算量はO(NlogN)
template <class T> void unique(std::vector<T> &v) {
  std::sort(v.begin(), v.end());
  v.erase(std::unique(v.begin(), v.end()), v.end());
}


#line 2 "main.cpp"

long long solve(long long A, long long B, long long C, long long D, long long E) {
  ll num = A * (B - C);
  ll ans = num == 0 ? 0 : D;
  ll X = D;
  FOR(i, 2, num + 1) {
    if (i % 10 == 0) {
      if (E <= X) {
        ans += X - E;
        X = X - E;
      } else {
        ans += X;
        X = X;
      }
    } else {
      ans += X;
      X = X;
    }
  }
  return ans;
}

// generated by online-judge-template-generator v4.7.1 (https://github.com/online-judge-tools/template-generator)
int main() {
  long long A, B, C, D, E;
  std::cin >> A >> B >> C >> D >> E;
  auto ans = solve(A, B, C, D, E);
  std::cout << ans << std::endl;
  return 0;
}